In broadcast systems, video and audio data are transmitted between N originating sources to M destination sinks. Such systems cannot easily rely on packet networking technology because of the need for synchronization of the data. The sources may be recording from CD players, live feeds, digital video files, etc. The control of a broadcast facility may involve rapid switching between many such sources and sinks. Presently, there are three types of routers that are used for such systems: space multiplexing, time multiplexing, and a combination of the two. In space multiplexing, a different physical channel is formed between the source and sink as in a classic telephone switching system. In time multiplexing, all sources and all sinks are connected to the same physical channel, each using a different time slot or slots. In combination systems, the endpoints obtain time-slotted data on multiple physical channels.
When a switching system grows in terms of the number of sources and sinks it must handle, problems attend all three different kinds of systems. In time multiplexed systems, the bandwidth of the common physical channel has to be increased in proportion with the number of routes sharing the channel. Also, each connected device must be connected to the physical channel which presents interference and signal attenuation problems as the physical channel's frequency rises. In space multiplexed systems, the complexity of the switch increases geometrically as the number of endpoints rises. This is because each source must be selectively connectable to each sink, so the number of possible paths grows exponentially with the number of sources and sinks.
There is a perennial need for switches that handle digital data synchronously, and that must remain time aligned, that do not grow in complexity too fast as the endpoint capacity of the switch increases.